The pilot was returning to land after a period of thermalling flight, when severe turbulence was encountered. The pilot's head hit and broke the canopy, and he then had problems with his vision. Heavy sink was also experienced. The pilot stated his last recollection of events was making a left turn towards the airfield at about 150 feet above the ground, and then regaining consciousness in the wreckage. Investigation revealed that the glider had touched down on a 5 metre wide strip between areas of cane growing to about 1.7 metres in height. The left wing caught in the cane and the aircraft slewed violently before coming to rest with the wing completely torn out of the fuselage.